1. Field of the Invention
The present invention relates to a method of forming fine patterns on a substrate. It particularly relates to the use of the evanescent wave to fabricate a desired fine pattern on a substrate by forming microstructures by using a laser beam to control the motion of atoms and molecules to deposit the atoms or molecules on the substrate.
2. Description of the Prior Art
The forming of submicron patterns using an optical reduction system is used extensively in the production of semiconductor integrated circuits. In this method, the surface of an object used to form the fine pattern is coated with a photosensitive resist and the optical reduction system is used to burn the fine pattern. Then, using the photosensitive resist layer as an etching mask, the surface of the object is etched to remove portions of the resist layer that are not required, thereby forming the required fine pattern. A drawback of this method is that the resist contains minute amounts of impurities that diffuse into the surface of the object used to form the pattern, affecting the electrical characteristics. There is also a method of forming a fine pattern by using a focused electron beam. However, inasmuch as this method involves sequential exposure and therefore involves the use of a photosensitive resist, it has the same problem.
Recently, there is a method that has attracted attention that uses the interaction between an optical standing wave and electrically neutral atoms. For example, Reference 1 (G. Timp, et al., xe2x80x9cUsing Light as a Lens for Submicron, Neutral-Atom Lithographyxe2x80x9d, Phys. Rev. Let., 69, 1636-1639, 1992) describes, with reference particularly to the configuration shown in FIG. 1 of the reference, by using a laser beam having a wavelength of 589 nm to form a standing wave with a diameter in the order of 300 xcexcm, through which is passed an orthogonal beam of atoms having a average velocity of 740 m/s, it should be possible to form lines having a width in the order of 10 nm. Also, in Reference 2 (A. S. Bell, et al., xe2x80x9cAtomic Lithographyxe2x80x9d, Microelectronic Engineering 41/42, 587-590, 1998), with particular reference to the configuration of FIG. 1(a) of said reference, there is described the use of two reflectors and a 425-nm laser beam to produce a standing wave with a grating-shaped pattern, which is used to form a clearly separated atomic dots in quadratic lattices with a period that is two-thirds the wavelength of the light used (283.7 nm). A beam of chromium atoms was generated and laser-cooling technique was used to collimate the beam in the transverse direction of atomic motion, a feature being the use of a laser beam having a wavelength close to the wavelength at which chromium atoms undergo resonance transitions.
It is well-known that in the interaction between atoms and optical field, when a laser is used having a wavelength that is longer than that at which the atoms undergo resonance transitions, the atoms are subjected to a dipole force urging them towards regions of high optical intensity within the laser beam. Conversely, when a laser is used having a wavelength that is shorter than the wavelength at which the atoms undergo resonance transitions, the atoms are subjected to a dipole force urging them away from regions of high optical intensity within the laser beam. In the case of Reference 2, the dipole force mentioned above is used to form the pattern on the substrate. A feature of the method is that since it does not employ a photoresist, there is no contamination of the silicon substrate surface. In the case of fine pattern forming methods of the prior art, as described in the above References 1 and 2, line-shaped or dotted patterns are produced, but because a standing wave is used, applications of the methods are limited. Even if in the future this limitation should be improved, the methods will still be limited to simple shapes such as polygons.
An object of the present invention is to provide a method of forming a fine pattern in one operation, using interaction between light and atoms.
For achieving the above object, in accordance with a first aspect, the invention provides a method of forming a fine pattern, the method comprising a step of projecting a predetermined electromagnetic wave at a first surface of an object in which the electromagnetic wave can propagate under conditions whereby the electromagnetic wave is totally reflected in the object, the first surface including at least a portion that is flat; a step of applying an intensity to an evanescent wave emitted from a second surface located at a position at which the total reflection occurs that corresponds to the position of the second surface; a step of irradiating a gas at the second surface, a kinetic energy of constituent elements of the gas being less than an energy of interaction between the evanescent wave and the constituent elements of the gas; and a step of adsorbing a portion of the constituent elements of the gas on the second surface.
In accordance with a second aspect in which a mask is used in adsorption of other atoms or molecules, the method comprises a step of projecting a predetermined electromagnetic wave at a first surface of an object in which the electromagnetic wave can propagate under conditions whereby the electromagnetic wave is totally reflected in the object, the first surface including at least a portion that is flat; a step of applying an intensity to an evanescent wave emitted from a second surface that is a surface other than the flat plate surface portion that corresponds to the position of the second surface; a step of irradiating a gas introduced in proximity to the second surface, a kinetic energy of constituent elements of the gas being less than an energy of interaction with the constituent elements of the gas; a step of adsorbing as first adsorbents a portion of the constituent elements of the gas on the second surface; and a step of selectively adsorbing second adsorbents in accordance with an amount of the first adsorbents.
In accordance with a third aspect in which the intensity of the incident electromagnetic wave is used to form a pattern, the method comprises, with respect to a beam of electromagnetic wave having a predetermined beam size, a step of applying an energy density level dependent on a position in a cross-section thereof; a step of inputting the beam to which an energy density level has been applied to a first surface of an object that can propagate the beam under conditions whereby the energy beam is totally reflected at a second surface; a step of irradiating a gas introduced in proximity to the second surface, a kinetic energy of constituent elements of the gas being less than an energy of interaction between an evanescent wave produced at the second surface and the constituent elements of the gas; and a step of adsorbing a portion of the constituent elements of the gas on the second surface corresponding to an intensity of the evanescent wave.
In accordance with a fourth aspect in which the intensity of the incident electromagnetic wave is used to form a pattern and a mask is used in adsorption of other atoms or molecules, the method comprises, with respect to a beam of electromagnetic wave having a predetermined thickness, a step of applying an energy density level dependent on a position in a cross-section thereof; a step of inputting the beam to which an energy density level has been applied to a first surface of an object that can propagate the beam under conditions whereby the energy beam is totally reflected at a second surface; a step of irradiating a gas introduced in proximity to the second surface, a kinetic energy of constituent elements of the gas being less than an energy of interaction between an evanescent wave produced at the second surface and the constituent elements of the gas; a step of adsorbing a portion of the constituent elements of the gas on the second surface corresponding to an intensity of the evanescent wave; and a step of selectively adsorbing second adsorbents in accordance with an amount of the first adsorbents.
In accordance with a fifth aspect in which monochromatic light is utilized to draw a pattern, the method according to the first or second aspects in which the step of applying an intensity to an evanescent wave emitted from a second surface located at a position at which the total reflection occurs that corresponds to the position of the second surface includes a step of using a laser beam to project a hologram image at the position of the first surface and applying an intensity to an electromagnetic wave.
In accordance with a sixth aspect which is convenient for forming a particularly large pattern, the method according to the first or second aspects in which the step of applying an intensity to an evanescent wave emitted from a second surface located at a position at which the total reflection occurs that corresponds to the position of the second surface includes a step of projecting a mask image relating to transmission of a predetermined electromagnetic wave at the position of the first surface and applying an intensity to the predetermined electromagnetic wave.
In accordance with a seventh aspect in which a plate structure is used that forms a pattern on the surface, the method according to the first or second aspects in which the step of applying an intensity that corresponds to the position of the second surface includes a step of applying an intensity to a predetermined electromagnetic wave corresponding to change in a thickness position of the object.
In accordance with an eighth aspect in which electromagnetic wave interference can be used to control transmissivity, enabling an incident electromagnetic wave intensity pattern to be provided, the method according to the first or second aspects in which the step of applying an intensity to an evanescent wave emitted from a second surface that corresponds to the position of the second surface includes a step of applying an intensity to a predetermined electromagnetic wave corresponding to positional change in transmissivity of the electromagnetic wave in the object.
In accordance with a ninth aspect in which an incident electromagnetic wave intensity pattern can be provided using positional change in surface reflectance, the method according to the first or second aspects in which the step of applying an intensity to an evanescent wave emitted from a second surface that corresponds to the position of the second surface includes a step of applying an intensity to a predetermined electromagnetic wave corresponding to a positional change in reflectance of the first surface.
In accordance with a tenth aspect in which an incident electromagnetic wave intensity pattern can be provided using positional change in surface light absorptivity, the method according to the first or second aspects in which the step of applying an intensity to an evanescent wave emitted from a second surface that corresponds to the position of the second surface includes a step of applying an intensity to a predetermined electromagnetic wave corresponding to positional change in light absorptivity of the first surface.
In accordance with an eleventh aspect in which in order to be able to perform the steps of adsorption and patterning separately and independently, the method of forming a fine pattern comprises a step of projecting a predetermined electromagnetic wave at a first surface of an object in which the electromagnetic wave can propagate under conditions whereby the electromagnetic wave is totally reflected in the object, the first surface including at least a portion that is flat; a step of applying an intensity to an evanescent wave emitted from a second surface located at a position at which the total reflection occurs that corresponds to the position of the second surface; a step of irradiating a gas at the second surface, a kinetic energy of constituent elements of the gas being less than an energy of interaction between the evanescent wave and the constituent elements of the gas; and a step of adsorbing a portion of the constituent elements of the gas on the second surface.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.